To a food processor bowl or blender container, add balsamic vinegar, lemon juice, garlic, sugar, and salt. Cover and process or blend to combine. With motor running, add oil in a steady stream.
In a salad bowl, combine mesclun and currants. Drizzle with enough dressing to lightly coat the salad. Sprinkle walnuts on top. Store remaining dressing, covered, in the refrigerator. Makes 6 side-dish servings.
You can find mesclun, a mixture of salad greens, in the produce section of large supermarkets.